In an another article I found this: "Although the cause for the epidemic remains unknown, theories suggest it could have been a deadly viral haemorrhagic fever exacerbated by the worst droughts to hit the region in 500 years.Heavy downpours that followed the drought saw an increase in populations of the Vesper mouse – a carrier of haemorrhagic fever.According to physician Francisco Hernandez, symptoms included high fever, severe headache, vertigo, black tongue, dark urine, dysentery, severe abdominal pain, head and neck nodules, jaundice and profuse bleeding from the nose, eyes, and mouth." So the haemorrhagic fever may have been indigenous and have nothing to do with European livestock?

What the actual study says is that the scientific team has found the DNA of Salmonella enterica in the dental pulp of human remains found in a burial site where cocoliztli victims supposedly were interred. Therefore they suggest that S. enterica should be further investigated as a strong candidate to be the pathogen that caused the epidemy of 1545. Difference between scientists and journalists is that the former present the results of their research as ongoing searchs for evidence, while the second jump to conclusions to write eye-catchy headlines.

Indeed, symptoms as described by the chronicles are consistent with acute forms of S. enterica infections. Together with the presence of S. enterica DNA in the dental pulp of victims of the epidemic, it makes it a compelling suspect.

On the other hand, many other infections can cause similar symptoms and it is also known that S. enterica, as many other bacteria, is opportunistic. The Spanish Flu epidemic, for instance, presented cases where Haemophillus influenzae (Pfeiffer Bacillus) was present; actually, doctors at the time thought it was the pathogen that was causing the epidemic, and developed vaccines against it. It was identified in autopsies of influenza victims, so it became, for a while, the prime suspect. However, in time, it was proved that the bacillus was just opportunistic, taking advantage of compromised immune systems. It wasn't until 2005 that a team of researchers was able to sequence the DNA of the H1N1 virus strain -later the disease was replicated in monkeys-.

Ancient epidemics are notoriously difficult to accurately diagnose. The Athens Plague, Justinian's Plague, Black Death, ecc, are well known and documented, but debate over the pathogen that caused them is still ongoing. Even in the case of the Black Death not all researchers are convinced that Yersinia pestis was the culprit, and the Black Death is, probably, the most intensively researched historical pandemics.

I had seen a presentation that suggested Hanta (sp?) virus. The drought and deluge were about the same as outbreaks in this country ? Adding to the problem that the people were crowded into a barracks kind of living ?